Which source should I use in a dvd duplicator?
 

I am going to build a dvd duplicator as described elsewhere in this forum (Wytron 399 controller, 9 Pioneer 111D burners, Lite On dvd rom, and WD Hard drive). I use Encore DVD for my authoring, and in the past have always burned dvds from an image file (.iso extension). Can I use an image file with the duplicator, or do I use an already-burned dvd as my source, or can I go either route? Thanks for any help on this.

extended question for DVD burning
 

Also, is it best to burn all the DVD's directly from the program (i.e. PPro or Encore) or does making a copy from the first burned copy work just as well.